Electrical protective system



Nov. 15, 1927.

1,649,025 .C. LE G. FORTESCUE ELECTRICAL PROTECTIVE SYSTEM Filed Dec. 17, 1925 ower Conducfors. l v

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- BY 'ATT NEY Patented Nov. 15, 1927.

UNITED STAT -s PATENT oF- lca.

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SYLVAINIL.

Application filed December 17, 1925. Serial-Ito. 75,994. i

An ob ect of my invention is the minimiz- I ing'of acoustic shock intelephone receivers by so dissipating the energy transmitted through the telephone circuit that the receivers are not afiected thereby. v

Another object of my invention is to protect telephone or other signal circuits and apparatus. from undue voltage strains.

I 115 It is now Well understood that in a power system, for example, operating with a solidly grounded neutral, an abnormal condition, such as a fiashover to ground, causes a singlephase current to flow i-na circuit comprising the grounded conductor, the fault, the ground circuit and the neutral connection.

This flow of current maybe sufficient to induce a high voltage in an adjacent lntelhence-transmission circuit, the magnitude of which depends upon the value of the induc-- ing current, thev proximity of the power and V intelligence-transmission circuits, conditions of the soil, the impedance ofthe telephone circuit and, of course, the duration of the disturbance.

-. The interference effect of the voltage thus;

induced in a telephone circuit, for example,

varies with the magnitude thereof and'the effectiveness of the telephone protective apparatus. In many cases, severe magnetlc disturbance is produced in the telephone receivers with a corresponding acousticshock to the operators. -Excess1ve voltage may also cause failure of insulation or other wise 40 effect relays and signal devices. Various devices have been employed, such as carbon-block protectors; for discharging the induced ener through a grounded circuit. The effectiveness of such devices is limited by their inherent defects. It has been found that carbon-block protectors inev'itably fail to ground both sides of the telephone circuit simultaneously, whereupon severe vibrations are set u in the telephone receivers, -which eflect as been termed acoustic shook.

In order to overcome this faulty operation of protectors of the above-indicated char- Wet, an method new p y d c p se the connection of a drainage coil between the telephone conductor with the neutral or midpoint of the coil grounded. This con-- 1166111011 1s olnectronable in that it affords an electrical connection between the different hues of the telephone. circuit and thereby increases the transmission losses and inter feres with the balancing and, testing of the telephone or signal lines.

In accordance with my invention, I employ a drainage coil that is n'ormall openclrcuited; that is, it. is not normal yconnected in circuit with the telephone conductors.

My invention will be best understood by reference to the accompanying drawing, in which the singlefigure is a diagrammatic representation of circuits and apparatus embodying my invention.

Referring to the drawing, the power circuit, comprising line conductors 1,2 and 3, is illustrated as a polyphase circuit having a grounded neutral connection through a con-' ductor 4:. Adjacent to and paralleling the "power conductors, is a telephone circuit, for

example, comprising conductors 5 and 6 and a telephone terminal equi ment including a receiver 7. At a point a ong the telephone circuit is installed protective apparatus comprising a drainage coil 8 wound in two substantially equal parts, or sections, 9 and 10,

'upon a common magnetic core 11.

In accordance with this construction, a voltage induced in winding 9 *will induce a corresponding potential in winding 10. These windings are, respectively connected through suitable gap protectors 12 and 13 to line conductors 5 and 6. At another point along the telephone line similar protective apparatus is installed comprising a drainage coil l i'and spark gaps 15 and 16. The coil phone conductors 5 and 6, which may be.

presumed to be of sufficient value to break down and thereby establish a circuit through the spark-gap protectgr 12, the drainage coil 14 has two sections 18 and 19 that are wound winding 9 to ground, and thence through portion 19 of coil 14 and gap 16.

It will be evident that the current flowing in windings 9 and 19 immediately induces a current at a corresponding high voltage in windings 10 and 18, respectively, and results in break-downs across the protectors 13 and 15. The breakdown of protectors 13 and 15 is substantially simultaneous with the breakdown of protectors 12 and 16, the diiference in time being so small that the mechanical inertia of the dia hragm of the receiver 7 does not permit 0 an appreciable vibration therein within the time interval required for dissipating the energy from the telephone circuit to ground.

In a long telephone system, it may be advisable to install more thantwo drainage coils. It has also been found advantageous to employ a spark-ga structure of .the character described in atent No. 1,509,497

Y -to Joseph Slepian, which device produces a brush discharge between its confronting surfaces and a uniform discharge of energy.

I have also found it advantageous to con- .nect an additional spark gap arrester across the terminals of each drainage coil, as lllustrated at 21 and 22. In the event of apower conductor falling on a telephone line, a very high voltage would be impressed on the drainage coils except for the fact that the protectors 21 and 22 will break down. and so limit the impressed voltage to a safe value, thus preventing damage to the coils.

Various modifications may bemade in my invention and its application, as will be readily appreciated by those skilled in'the art. I desire, therefore, that my invention shall be limited only in accordance with the scopeof the appended claims.

I claim as 'my invention 1. In a protective system for an intelligence-transmission circuit running adjacent to a power-circuit, the combination with a pair of conductors, of a normally open-circuited drainage coil, means for grounding one point of said coil, and means for connecting said coil between said conductors under predetermined voltage conditions.

2. In a protective system for telephone conductors running adjacent to a power circuit, the combination with a pair. of telephone conductors, of a pair of normally open-circuited drainage coils means for grounding the junction point of said coils, and means for connecting said coils between said conductors under predetermined voltage conditions.

3. In a protective system for telephone conductors running adjacent to a power circuit, the combination with a pair of telephone conductors of a normally open-circuited two-part drainage coil, said parts being inductively related, means for grounding the mid-point of said coil, and means for connecting said coil between said conductors under predetermined voltage conditions.

4. In a protective system for telephone conductors running adjacent to a power circuit, the combination with a pair of telephone conductors, of a normally open-circuit'ed drainage coil, means for grounding the mid-point of said coil, and means comprising a spark gap arrester for connecting said coil between said conductors under predetermined voltage conditions.

5. In a protective system for telephone conductors running adjacent to a power circuit, the combination with a pair of telephone conductors, of a normally open-circuited two-part drainage coil, means for grounding the junction-point of said coil parts, and means comprising a spark gap arrester for connecting said coil between said conductors under predetermined voltage conditions.

6. -In a protective system for telephone conductors running adjacent to a power circuit, the combination with a pair of telephone conductors, of a normally 0 en-circuited two-part drainage 'coil, sai parts being inductively related, means for grounding the midpoint of said coil, and means comprising a spark gap-arrester for connecting'said coil between said conductors under predetermined voltage conditions.

7. In a protective system for an intelli-' gence-transmission circuit running adjacent to a power circuit, the combination with a pair of conductors, of a normally open-circuiteddrainage coil, means for grounding the mid-point of said coil, means for connecting said coil between said conductorsunder predetermined voltage conditions, and meiins for limiting the voltage across said 001 8. In a protective system for an intelligence-transmission circuit running adjacent to a power circuit, the combination with a pair of conductors, of a normally open-circuited drainage coil, means for grounding the mid-point of-said coil, means comprising a spark gap arrester for connecting said coil between said conductors under predetermined voltage conditions, and means comprising a spark gap for shunting said coil.

In testimony whereof, I havehereunto subscribed my name this 8th day of December, 1925.

CHARLES LE G. FORTESCUE. 

